Process for recovering heavy mineral by selective sedimentation from a body of flowing water

ABSTRACT

A process of recovering heavy minerals from a body of natural flowing water in which said minerals are entrained, comprising A. PROVIDING IN SAID BODY OF FLOWING WATER ADJACENT THE BOTTOM THEREOF A COLLECTING STRUCTURE WHICH IS CAPABLE OF PROMOTING A SELECTIVE SETTLING OF SAID HEAVY MINERALS FROM SAID BODY OF FLOWING WATER, B. ARTIFICIALLY AGITATING THE BOTTOM OF SAID BODY OF WATER UPSTREAM OF SAID COLLECTING STRUCTURE, THEREBY PRODUCING A SUSPENSION OF SAID HEAVY MINERALS AND MATERIAL OF LOWER DENSITY, C. PERMITTING SAID SUSPENSION TO FLOW DOWNSTREAM TO SAID COLLECTING STRUCTURE, WHEREBY SAID HEAVY MINERALS SELECTIVELY SETTLE IN SAID COLLECTING STRUCTURE AND THEIR PROPORTION TO TOTAL SOLIDS IN SAID COLLECTING STRUCTURES IS RAISED BEYOND THEIR PROPORTION IN SAID SUSPENSION, AND D. PERIODICALLY REMOVING THE SETTLED AND CONCENTRATED HEAVY MINERALS FROM SAID COLLECTING STRUCTURE. The collector comprises walls or bristles defining settling cells of limited depth into which heavier particles settle while lighter particles are carried along by the flowing water.

trite States aterit H iiering Aug. 28, 1973 [75] Inventor: NorbertHering, Frankfurt, Germany [73] Assignee: MetallgesellschaitAktiengesellschaft,

Frankfurt/ Main, Germany 22 Filed: Feb. '17, 1972' [21] Appl. No.:227,246

Related US. Application Data [30] Foreign Application Priority Data Aug.26, 1969 Germany P 19 43 301.3 Mar. 27, 1971 Germany P 2l l4 925.7

[52] US. CL, 299/8, 209/156, 209/458, 209/506 [5 l] int. Cl. E2: 45/00[58] Field of Search 299/8; 209/156, 447, 209/454, 458, 483-486, 506

[56] References Cited UNITED STATES PATENTS 416,626 12/1889 lrvin209/485 X 2,272,005 2/1942 Hudson 209/458 2,926,786 3/1960 Craft etal..... 209/506 X 14,847 5/1856 Auld et al. 209/506 157,192 11/1874Campfield et al. 209/458 ll/l952 3/1937 Vogelpoel 299/8 X Silke 299/8Primary Examiner-Ernest R. Purser Attorney-Ralph D. Dinklage and ArnoldSprung ABSTRACT A process of recovering heavy minerals from a body ofnatural flowing water in which said minerals are entrained, comprisinga. providing in said body of flowing water adjacent the bottom thereof acollecting structure which is capable of promoting a selective settlingof said heavy minerals from said body of flowing water,

b. artificially agitating the bottom of said body of water upstream ofsaid collecting structure, thereby producing a suspension of said heavyminerals and material of lower density,

c. permitting said suspension to flow downstream to said collectingstructure, whereby said heavy minerals selectively settle in saidcollecting structure and their proportion to total solids in saidcollecting structures is raised beyond their proportion in saidsuspension, and

d. periodically removing the settled and concentrated heavy mineralsfrom said collecting structure. The collector comprises walls orbristles defining settling cells of limited depth into which heavierparticles settle while lighter particles are carried along by theflowing water.

13 Claims, 5 Drawing Figures Patented Aug. 28, 1973 4 Sheets-Sheet lPatented Aug. 28, 1973 3,754,789

4 Sheets-Sheet I5 dz'rec/mn 0f flaw Patanled Aug. 28, 1973 4Sheets-Sheet 4 b cm 3 BE S 9 mg 0 S 3856 o iniiif /m em0r Narber/Her/77g has;

PROCESS FOR RECOVERING HEAVY MINERAL BY SELECTIVE SEIDIMENTATION FROM ABODY OF FLOWING WATER This application is a continuation-in-part ofapplication Ser. No. 66,551, filed Aug. 24, 1970, now abandoned. I

This invention relates to a process of recovering heavy minerals frombodies of flowing water by selective sedimentation.

In the shelf areas of the sea near the coast, a continuous sedimentationprocess is taking place because solids are entrained in considerableamounts in rivers or sea currents having a constant direction orperiodically changing directions and selectively settle from the body offlowing water as a result of differences in density when the velocity offlow falls below a lower limit.

For instance, aerial photographs of the mouth of the Mississippidischarging into the Gulf of Mexico reveal clearly by the differentcolor that the stream carries entrained solids into the Gulf over adistance of more than sixty miles.

A deposit known as placer may be formed in river valleys or in shelfareas by the eluviation or sedimentation of minerals having a highspecific gravity. The resulting deposits of so-called mineral placers oralluvial ore constitute enriched heavy minerals, which have beendetached by the abrasive action of rivers from inland areas or of thesurf from the coast and have been carried offshore by the entrainingforce of the water. Marine currents often flow parallel to the coast andfurther sort the weather-wom debris, which have been presorted duringthe first sedimentation. 7

Such deposits will be formed where the conditions at the floor of thebody of water are such that rising of settled particles due toturbulence has been prevented. The deposits may be disposed in shelfareas which are on a lower level and/or remote from the coast if theyoriginated in a preglacial period and were not subjected to the sortingaction of marine currents.

In a few exceptional cases the sorting'due to the flowing current hasresulted in such a concentration that the allocthonous deposit could beeconomically mined. For instance, tin stone is mined off the coast ofComwall (Great Britain), Thailand and- Indonesia. Magnetite is recoveredfrom the bottom of the sea in the shelf areas of Japan.Diamond-containing sands are mined off the coast of South West Africa.

A periodically renewing deposit of shells is periodically mined off thewest coast of Iceland. During the winter, a fairly strong, uniform westwind produces an ocean current in a direction from west to east so thatlarge amounts of shells of a species of oyster are carried into anatural basin behind a geological barrier.

That deposit is exploited in the summer by dredging and is processed tobuilding materials.

Heavy mineral deposits are often found in natural caverns in rock areasat the bottom of the sea.

The formation of such allochthonous deposits has already been simulated,e.g., in the washing of gold. In Malaysia, tin stone is recovered fromrivers having a small gradient by means of thick planks placed into theriver transversely to the direction of flow. A classical example hasbeen told in the Greek myth of the Golden Fleece. Sheep skins wereplaced into a river in which gold was entrained and the heavy goldparticles were preferentially collected in the skins. The concentrationof heavy minerals from mixtures containing them by jigging has beentaught by dressing technology for a very long time. The variety of knownjigging machines indicates that a concentration of minerals, byselective sedimentation from flowing liquids depends on a large numberof controlling factors, which must be matched in each case. In manycases, empirical findings are more advanced than theory.

It is generally accepted that during a sedimentation process the varioussolid particles in a flowing liquid separate as a result of theirdifferent velocities of fall. These velocities depend on the density andsize of the particles. For instance, tin stone having a density d ofabout 7 grams per cubic centimeter and a given particle size will settleout of a liquid current which entrains quartz sand grains having threetimes the volume of the tin stone particles and a density d of about 3grams per centimeter.

A concentration of relatively heavy minerals by sedimentation to form adeposit is possible only in areas where shallow layers which have beenformed are not continually removed and distributed by continuous orperiodic currents which are superimposed on the main current and mayeven oppose the same.

Such deposits can form on the bottom of bodies of flowing liquid onlywhere such bottom has a surface structure which prevents an agitation ofparticles once they have been settled.

There are only very few locations where both requirements, namely, thepresence of a current in which heavy minerals are entrained and thepresence of a surface structure which promotes the sedimentation ofheavy minerals at the bottom of the flowing liquid, are met.

In connection with placer deposits in rivers, a current having aconstant direction and a velocity of flow varying at a low frequency maybe expected. In the shelf areas, the tide will result in more frequentchanges of the direction of flow and also in more frequent changes ofthe velocity of flow. A study of placer deposits and experience madewith jigging machines have led to the recognition that suitableartificial changes of the bottom of the bodyof flowing water,particularly the bottom of the sea, will promote a selective settling ofheavy minerals from liquid currents in which these minerals areentrained. The invention is based on that recognition.

It is an object of the invention to provide an improved process ofrecovering heavy minerals from bodies of flowing water by selectivesedimentation.

The process according to the invention is characterized in thatartificial collecting structures are placed on or upwardly adjacent tothe bottom of the body of flowing water and the heavy mineralsselectively collected by said collecting structures are removedtherefrom from time to time.

The artificial collecting structures should have, such tially exceedtheir vertical depth. The collecting structures may consist, e.g., ofstrips of material having regularly spaced slots, which extend halfwayacross the strip, and assembled to define triangular or quadrangularsettling cells, or of radially connected tube sections, which arecircular or polygonal in cross-section. Another embodiment of thecollecting structure according to the invention may be made from plasticmaterial and is similar to a brush. it may consist, e.g., of a mat ofsynthetic thermoplastics provided with regularly distributed, preferablyvertical bristles, which define the settling cells.

The mat is suitably provided with bristles having different lengths andbristles within a given length range are spaced equal distances apart.For instance, the short bristles may have a length of -15 centimetersand a width of 0.5-3 millimeters and may be spaced 0.5-3 millimetersapart whereas the long bristles have a length of -60 centimeters and awidth of 0.5-2 millimeters and are spaced apart on the mat about 3-30centimeters.

The substantially two-dimensional collecting structures are placed onthe bottom of the body of flowing water in suitable areas and areanchored in known manner by weights. They may be used to cover an areaof an order of several square meters to square kilometers. The heavyminerals collected in the settling cells of the artificial collectingstructures may be recovered from time to time by means which areconventional in marine engineering, such as suction dredgers, air-liftpumps or hydrojet pumps.

The artificial collecting structures used according to the invention areplaced in areas in whichthe existing flow is at least temporarilycapable of carrying the heavy mineral to be recovered to the collectingstructure. The collecting structure may have such a surfaceconfiguration that it will reduce excessive velocities of flow. Thevelocity of a continuous unidirectional cur rent may be reduced by afixed collecting structure which includes an angle of incidence up toabout 30 with the direction of flow.

The artificial collecting structures need not uniformly cover'the entirearea which has been selected as a settling area. It will be sufficientif the above mentioned, substantially two-dimensional structures arespaced apart in the settling area. In that case, the spaces between theindividual structures should not be substantially larger than thesettling cells. Collecting structures of different configuration may beplaced in one and the same settling area. Each substantiallytwodimensional collecting structure may constitute a combination of ahoneycomb consisting of tube sections, car tires or slotted strips, onthe one hand, and a brushlike mat, on the other hand; in that case, themat forms the bottom of the collecting structure. The collectingstructures need not be placed on the bottom of the body of flowing waterbut in dependence on the location of the current to beexploited may bespaced to some extent above the bottom. Brushlike mats are particularlysuitable for this purpose.

The collecting structures used according to the invention retard theflow at their surface so that the slurry which enters the settling cellsof the collecting structures is caused to settle under temporarilystagnant conditions. In that process, the flowing water is both a sourceof energy and an entraining agent and in an operation which requires noattendance and little maintenance ensures a supply and classification ofthe solids.

The process according to the invention may be used to advantage torecover valuable heavy minerals which 5 justify a certain capitalinvestment. Such minerals are,

e.g., monazite, cassiterite (tin stone), tantalite, ilmenite, rutile,zircon, magnetite, garnet, noble metals (gold) and precious stone(diamond).

The discovery of suitable conditions of flow and suitable settling areasis a joint task of hydrologists and prospectors. These two sciences dofurnish the information which is essential for the working of theinvention.

The artificial collecting structures used according to the inventionshould consist of a material which resists sea water and should bemovable at a reasonable expense to the area in which they are to belowered. Suitable materials are plastic-coated metals, concrete, andplastics.

The form and combination of the collecting structures used in a givencase will depend on the ratio between the expenditure and the results.For a recovery of highly valuable heavy minerals, more expensiveartificial collecting structures may be used. Simpler types ofcollecting structures will be used to cover very large settling areas.

It has been found that selective sedimentation cannot be obtained unlessthe bottom of the body of water is disposed to enable a continuousentraining of material or the flow conditions result in an agitation ofsettled material from the bottom of the body of water. Theserequirements are not met in many cases.

This disadvantage can be overcome if the bottom of the body of water isartificially agitated in areas which are disposed upstream of theartificial collectingstructures.

In a preferred embodiment of the invention, the artificial agitation iseffected hydraulically or pneumatically. For this purpose, a jet ofwater or air under high pressure is directed into the deposit so thatthe material is released'from the structure in which it is looselybonded and enters the current of the overlying column of water. Thatcurrent may be due, e.g., to the tides.

Agitation may also be effected by the intermittent firing of placedexplosive charges.

The agitation may also be efi'ected by a mechanical working of thebottom of the body of water. Plows may be used for this purpose and maybe drawn through the bottom and towed, e.g., by a moving ship, or movedbetween two fixed stations. Wheels operating like hay tedders or forkwheels may be similarly used.

Instead of from a ship, the agitating equipment may be operated frombuoys or underwater stations. The energy of the water flowing past suchmeans may be transformed into a rotary movement mechanically orindirectly by a generator-motor assembly. The energy may also besupplied from the shore entirely or in part. In larger areas, e.g., incoastal shelves where a plurality of the units for artificial agitationare used, a central control may be adopted.

To ensure that the suspension which has been formed by the agitation issupplied as fully as possible to the artificial collecting structureswhich have been placed to cause a selective sedimentation, it is desiredto provide guide means. Such guide means may consist, e.g., of guideplates which may consist of metallic or nonmetallic materials and whichmay adjust themselves to appropriate positions in response to the flowconditions. Damor platform-like structures may also be used to provideflow channels.

It may be desirable to use flaps which are disposed very close to thecollecting structures which intermittently act on the flowing water soas to transform the continuous current of water into. pulsating surgesof water whereby sediment having a lower specific gravity is displacedand an enriching of the heavy mineral component is promoted.

Some embodiments of artificial collecting structures arediagrammatically shown by way of examples in the drawings, in which FIG.1 is a top plan view showing a collecting structure which consists ofinterfitted crossjng strips having regularly spaced slots extendinghalfway across the strips.

FIG. 2 is a top plan view showing a collecting structure which isassembled from tube sections having a polygonal cross-section.

FIG. 3 is a vertical sectional view taken on line E-F of FIG. 2.

FIG. 4 is a top plan view showing a collecting structure assembled fromworn-down car tires.

FIG. 5 is a brushlike collecting structure made of plastic material.

The embodiment shown in FIG. 1 consists of crossing strips 1 and 2,which have the same width and at the regularly spaced intersections areprovided with slots extending halfway across the strip. The crossingstrips are interfitted like strips in packages for electric bulbs, fruitor eggs. The strips may consist of plastic material, plastic-coveredmetal or the like. The interfitted strips are firmly clipped together atthe intersections. The resulting structures are lowered to the bottom ofthe body of flowing water and secured by ropes 5 to heavy anchoringelements 4. In this embodiment, the settling cells 6 may be triangularor quadrangular. For settling cells having a side length of about 50centimeters, it is recommended to use strips whichare about 40-60centimeters wide.

The same reference characters as in FIG. 1 are used in FIG. 2, whichshows an embodiment consisting of tube sections 11, which have apolygonal cross-section and preferably the same length. The tubesections 11 may be connected by bolts 12 or the like to form asubstantially two-dimensional structure, which forms an element of anartificial collecting structure. These elements may be placed on thebottom of the body of water in the selected settling area and may beconnected, e.g., by ropes 13 to heavy anchoring elements 14.

FIG. 3 is a vertical sectional view of the structure of FIG. 2 but isanalogously applicable to the structure of FIG. 1. FIG. 3 indicates alsoa combination of honeycomb and brushlike structures because it shows amat 15 provided with bristles 16.

The collecting structure shown in FIG. 4 is assembled from worn-down cartires 21. The tires may be packed together as closely as possible, as isshown, so that the points of contact between three adjacent tires lie onan equilateral triangle and each tire contacts six other tires. Inanother arrangement, each tire may contact only four other tires. Thetires may be connected by rivets 22 or by stitching by means of arope ofwire or plastic material at the points of contact between the tires.

In the embodiment shown in FIG. 5, a substantially two-dimensionalcollecting structure consists of a brush-like structure of plasticmaterial. A mat 31 carries bristles, which are preferably equally spacedapart on the mat and define the corners of the settling cells. Thesebristles may have diflerent lengths so that there are short bristles 32and long bristles 33, the latter being spaced larger distances apart.

The heavy minerals settle preferentially between the closely spacedshort bristles 32, which have a length of about 5-15 centimeters and arespaced apart by a distance which is ofthe order of the thickness orwidth of the bristles. The longer bristles 33 have a length of .about-50 centimeters and are regularly spaced about 3-l5 centimeters apartover the substantially two-dimensional structure and retard the flowover the settling cells. The small particles of the heavy mineral enterthe settling cells between the short bristles so that these particlesare substantially removed from the influence of changes in the flowconditions. The coarser particles of the lighter mineral remain adjacentto the longer bristles and are entrained by the flowing liquid underchanging conditions. V

FIG. 5 illustrates this differential behavior of particles which differin size and'density by the representation of heavy particles 35 by solidor black areas and of light particles 34 by white areas. The heavyparticles which are collected between the short bristles 32 in thecourse of time may be recovered by a suction operation in suitableintervals of time, e.g., twice to four times a year.

A honeycomb of joined automobile tires as shown in FIG. 4 on abed overwhich a river flows at about 2 miles an hour in combination withdynamite charges once a month at distances from one'to five milesupstream of the collector serves to enrich the proportion of solids ofhigh specific gravity to total solids within the collectors incontrastwith the proportion of such material to total solids just belowsuch collectors.

It will be appreciated that the instant specification and examples areset forth by way of illustration and not limitation, and that variousmodifications and changes may be made without departing from the spiritand scope of the present invention.

What is claimed is: v

I. A process of recovering heavy minerals from a body of natural flowingwater in which said minerals are entrained, comprising a. providing insaid body of flowing water adjacent the bottom thereof a collectingstructure which is capable of promoting a selective settling of saidheavy minerals from said body of flowing water,

b. artificially agitating the bottom of said body of water upstream ofsaid collecting structure, thereby producing a suspension of said heavyminerals and material of lower density,

c. permitting said suspension to flow downstream to said collectingstructure, whereby said heavy min.- erals selectively settle in saidcollecting structure and their proportion to total solids in saidcollecting structures is raised beyond their proportion in saidsuspension, and

d. periodically removing the settled and concentrated heavy mineralsfrom said collecting structure.

2. A process as set forth in claim 1, in which said collecting structurecomprises means for reducing the velocity of the water.

3. A process as set forth in claim 1, in which said collecting structureis provided in a body of water flowing continuously in a substantiallyconstant direction and said collecting structure is placed to define anangle of incidence up to 30 with said direction.

4. A process as set forth in claim 1, in which said collecting structuredefines a multiplicity of horizontally adjacent settling cells and eachof said cells has a predetermined vertical dimension and a maximumhorizontal dimension which does not substantially exceed said verticaldimension.

5. A process as set forth in claim 4, in which said collecting structurecomprises strips formed with regularly spaced slots extending halfwayacross the strips and said strips are assembled to define polygonalsettling cells.

6. A process as set forth in claim 4, in which said collecting structurecomprises vertical tube sections of about the same height and radiallyconnected to each other.

7. A process as set forth in claim 4, in which said collecting structurecomprises radially connected annular hollow bodies having generallyvertical axes and a slotted inside peripheral wall.

8. A process as set forth in claim 4, in which said collecting structurecomprises a mat having bristles extending upwardly therefrom anddefining said settling cells.

9. A process as set forth in claim 8, in which said mat is provided withshort and long bristles extending upwardly from said mat, said shortbristles are regularly spaced and define said settling cells, and saidlong bristles are also regularly spaced.

10. A process as set forth in claim 1, in which the agitation of thebottom of the body of water of step (b) is performed hydraulically orpneumatically.

11. A process as set forth in claim 1, in which the agitation of thebody of water of step (b) is performed by explosive charges.

12. A process as set forth in claim 1, in which the agitation of thebottom of the body of water of step (b) is performed by mechanicalworking.

13. A process as set forth in claim 1, in which the supply of saidsuspension of step (c) is promoted by flaptype means which producepulsating surges of water.

1. A process of recovering heavy minerals from a body of natural flowingwater in which said minerals are entrained, comprising a. providing insaid body of flowing water adjacent the bottom thereof a collectingstructure which is capable of promoting a selective settling of saidheavy minerals from said body of flowing water, b. artificiallyagitating the bottom of said body of water upstream of said collectingstructure, thereby producing a suspension of said heavy minerals andmaterial of lower density, c. permitting said suspension to flowdownstream to said collecting structure, whereby said heavy mineralsselectively settle in said collecting structure and their proportion tototal solids in said collecting structures is raised beyond theirproportion in said suspension, and d. periodically removing the settledand concentrated heavy minerals from said collecting structure.
 2. Aprocess as set forth in claim 1, in which said collecting structurecomprises means for reducing the velocity of the water.
 3. A process asset forth in claim 1, in which said collecting structure is provided ina body of water flowing continuously in a substantially constantdirection and said collecting structure is placed to define an angle ofincidence up to 30* with said direction.
 4. A process as set forth inclaim 1, in which said collecting structure defines a multiplicity ofhorizontally adjacent settling cells and each of said cells has apredetermined vertical dimension and a maximum horizontal dimensionwhich does not substantially exceed said vertical dimension.
 5. Aprocess as set forth in claim 4, in which said collecting structurecomprises strips formed with regularly spaced slots extending halfwayacross the strips and said strips are assembled to define polygonalsettling cells.
 6. A process as set forth in claim 4, in which saidcollecting structure comprises vertical tube sections of about the sameheight and radially connected to each other.
 7. A process as set forthin claim 4, in which said collecting structure comprises radiallyconnected annular hollow bodies having generally vertical axes and aslotted inside peripheral wall.
 8. A process as set forth in claim 4, inwhich said collecting structure comprises a mat having bristlesextending upwardly therefrom and defining said settling cells.
 9. Aprocess as set forth in claim 8, in which said mat is provided withshort and long bristles extending upwardly from said mat, said shortbristles are regularly spaced and define said settling cells, and saidlong bristles are also regularly spaced.
 10. A process as set forth inclaim 1, in which the agitation of the bottom of the body of water ofstep (b) is performed hydraulically or pneumatically.
 11. A process asset forth in claim 1, in which the agitation of the body of water ofstep (b) is performed by explosive charges.
 12. A process as set forthin claim 1, in which the agitation of the bottom of the body of water ofstep (b) is performed by mechanical working.
 13. A process as set forthin claim 1, in which the supply of said suspension of step (c) ispromoted by flap-type means which produce pulsating surges of water.